Biomechanics of juvenile tyrannosaurid mandibles and their implications for bite function

Abstract

The tyrannosaurids are among the most iconic dinosaurs described by science. Biomechanical data such as bite force allow for comparative analyses between established tyrannosaurid genera. The results of this study are used to infer mandible (lower jaw) strength at different growth stages, bases on estimates of jaw muscle forces the animals exerted. We found that mandibles of small/subadult tyrannosaurs experiences lower stress overall because muscle forces were relatively lower, but that mandibles experienced greater mandible stresses at decreasing sizes when specimen muscle force or surface area is normalized. Strain on post-dentary ligaments decreases stress and strain in the posterior dentary and where teeth impacted food. Tension from the lateral insertion of the looping m. (musculus) pterygoideus ventralis increases compressive stress on the angular but decreases anterior bending stress on the mandible. Lowered mid-mandible bending stresses are consistent with ultra-robust teeth and high anterior bite force in adult Tyrannosaurus rex. The results may be indicative of separate lifestyles and feeding mechanics between juvenile and adult tyrannosaurids. Juvenile tyrannosaurs were probably incapable of the bone-crunching bite of mature individuals and hunted smaller prey, while adult tyrannosaurs fed on larger prey items which they were better able to subdue.